Grinding process



Feb. 1, 1966 coEs, JR 3,232,010

GRINDING PROCESS Filed Aug. 20, 1963 W n /w l w// //////M" W ATTORNEY United States Patent 3,232,010` GRINDING PROCESS Loring Coes, Jr., Princeton, Mass., assignor to Norton Company, Worcester, Mass., a corporation of Massachusetts FiledAug. 20, 1963, Ser. No. 303,306 10,Claims. (,Cl. 51--281) This application is, a continuation-impart of oopending application Serial No. 253,966,V tiled January 25, 1963 entitled, Grinding Machine, now Patent No. 3,167,891, dated February `2, 1965 and of lits parent yapplication Serial No. 163,983, tiledlanuary` 3, 1962, now abandoned.

The invention herein relates to improving the eiciency of grinding operations, particularly to theincrease of the grinding ratio .of a given` grade. grinding wheel during its `operation on a workpiece.

For purposes of vmore detailedA background information, reference may be made; notfonly to the above applications, but also 4to thehandbook on Abrasives and Grinding Wheels, a publication |,by,and available from the Norton Company, Worcester 6, Massachusetts, which carries acopyright designation of 1954Y 1957, 19,58 `and 19.61 by the Norton Company. The contents of that handbook is hereby incorporatedI herein by reference, and al copy of the handbook is iiledfherewith for the-convenience of and to be retained `by" thePatent Oiiice in the file ofthis application,

The word grade as used herein relates tothe con,-

ventional meaningr thereof` inthe art of grinding, and` as indicated in` that handbook, is synonymous with:

strength of bonding. That; is, grade indicates the relative strength or holding power ofthe bond which holds the abrasive grades in place. Inl general, `with a given,

type` of bond,`it is the, amount of vbond which determinestlie strength of |bonding of a grindingwheel, i.e. its` grade, which is frequently referred to as hardness Definitions of grade may be fou-ndj on pages 1 2 and 70/ of the above referenced handbook.

Itl has 'been observed in conductingtests` to deter-mine the value of a series of various grinding wheels, that the plotted curve of their respectivegrinding ratios, after a while begins to. decrease with an` increase in, power, instead of continuing to increase. In conducting testsl to determine grinding wheel values under aiixed feed openasion such as described in the above mentioned application Serial No. 253,966, af series of different grades of grinding wheels, Le., wheels having structures varying the ratios of bond, abrasive,` porosity, are `run under xed feed conditions and the power required for` the fixed infeed is plotted las a function of the grinding ratio, which is the ratio of the volume of metal removed from the workpiece to the volume of wheel Wear during the grinding operation.

The resulting plot may be in concave in form, looking `from the ordinate along which power is plotted. That is, generally speaking, the grinding ratio initially may increase with power and then reach a maximum after `which it reverses and begins decreasing with a continued `increase in power. It must 1be remembered that such a curve results from testing a series of different grades of grinding wheels. Applicant, upon realizing` this situation initially and noting that on the low side of the maximum grinding ratio point the wheel grade was softer while on the 'high side thereof the wheel grade was` harder, suspected that the grinding ratio could be maximized merely by being more selective of the grinding grades. That is, that the grinding ratio could =be substantially increased if a wheel could be graded more narrowly so as to have its grinding ratio lie on the maximum point of the curve. It proved impossible, however, to effect this by present 3,232,016 carentes Feb. i, 196e manufacturing techniques. In other words, grinding grinding grade that applicant desired.

Surprisingly, however, applicant discovered that a grinding wheel of given grade which normally has a` grinding ratio below the maximum or curve reversal pointabove described, could be made to act slightly harder by a small increase in its speed to improve the grinding ratio substantially. Also, it was discovered that a grinding wheel whose normal performance is above the point of reversal in the curve, could have its grinding ratio also substantially increased by a slight decrease in its speed so as to make it act slightly softer. In other words, it was discovered that a given grade of grinding wheel may be made to appear to have a different hardness characteristic depending upon its operating speed, and that It is therefore the principal 'object of this invention to provide a process for improving the efficiency of a grinding operation by` a given grade grinding wheel on a workpiece during relative rotation thereof, -byl regulating a characteristic of the grinding operation, particularly the speed of the grinding wheel, while determining the grinding ratio, in order to increase that ratio toward the maximum possible `by effecting lan apparent change in the grade or hardness of the wheel during its operation.

Other objectsV and advantages of this invention will become apparent to those of ordinary skill in the art upony reading the following detailed description of the invention, in conjunction with the drawing, in which:

FIG-URE 1 is a diagram illustrating various dimensions in la surface grinding operation for determining grinding ratio; and

FIGURE 2 represents` apparatus for determining and visually indicating the grinding ratio and manuallylittle harder or a little softer than the actual specification therefor provides. Reference to the aforementioned handbook shows, for example on` pages 43 and 44 some standard maximum speeds for different types of grinding wheels for various types and strengths of bonds. It must be recalled, in reviewing these tables that grade refers to the strength of bonding, and that the type of bond and its low, medium or high strength indication therein may consequently be correlated with the various grades A to Z referred to on page l2 and particularly the soft, medium and hard indications on the page 22 chart. In other words, there is not only a standard maximum speed recommended by the manufacturer for any given wheel, but also as indicated on page 4l ofthe handbook, there is a recommended eflicient operating wheel speed in surface feet per minute. It is conventional and recommended to operate a purchased grinding wheel atsomewhere near the speed recommended by the maker, for the grain, grade and structure usually recommended for a grinding operation are based on the assumption that approximately the recommended Ispeeds will be employed. It was known, before this invention, that excessive speed may result in hard grinding action and that it may also introduce the danger of breakage. It was also known, as recommended on page 51 of the aforementioned handbook, that as the wheel wears smaller, its rpm. should be increased to maintain good cutting action and prolonged wheel life. However, not before the advent of this invention was there any appreciation that the grinding ratio of a given grade wheel may be substantially increased by regulating the speed of the wheel to make it act a little harder or a little softer than its actual specification indicates, by increasing or decreasing its speed respectively.

If a particular grade of wheel is operated until the abrasive becomes dull, it takes more power to accomplish metal removal, and the Wheel has an apparent harder feel or characteristic. This same effect of dulling may come about as the wheel tends to glaze by metal accumulating on the surface. If the surface becomes completely glazed, the wheel will have a much harder characteristic.

Conversely, 4a wheel of given grade that is driven into the workpiece with undue pressure is continuously broken down because it is being overworked. This characteristic is fully explained in the aforesaid application Serial No. 253,966, and is taken advantage of therein for dressing purposes. As the surface breaks down, the abrasive grits exposed are always the sharpest that can be presented, and the wheel has a :so-called softer cutting action. The present invention provides a way for operating a wheel at just the right degree of such breakdown to get the maximum metal removed for the particular grade of wheel being operated. lf the wheel is pushed too hard, it tends to breakdown and the grinding ratio falls oil". Similarly, if the wheels begin to load up or dull, the grinding ratio also falls off, because the metal removed then is less than at the most efficient rate. The ultimate in accordance with this invention is the maintenance of the grinding ratio at maximum, to insure the best quantity of metal removed consistent with the least wheel wear, by utilizing various parameters of the grinding operation, particularly constants and variables related to certain dimensions of the grinding wheel and workpiece, lfor determining when the wheel shall be speeded up or slowed down to accomplish the desired more efficient cutting action.

In the above mentioned application Serial No. 253,- 966, which is parent to the present application, there is set forth a way of determining the grinding ratio G, reference being made to FIGURES 9, and ll thereof. For purposes of a detailed explanation of one sort of exemplary equipment which may be employed to determine the grinding ratio, those figures are reproduced in the drawing hereof as FIGURES 1 and 2, the latter incorporating FIGURES l() and ll of that parent application.

It is to be appreciated while considering the detailed description below, that although surface grinding is referred to, all other types of grinding, including those mentioned on page 6 of the aforesaid handbook, are encompassed by this invention.

With reference to FIGURE l, it will be seen that a grinding wheel 10 which has an initial radius R, is disposed in a surface grinding operation relative to a workpiece 12, both the front and side view being illustrated in FIGURE l for convenience. The workpiece 12 has a length designated b and a width a, while the wheel has a thickness t in the direction of the Width a. Initially, the center 14 of wheel 10 is at a height H above a given fixed point, for example on workpiece 12 such as its base or table support line 16, but as the wheel operates it wears down and consequently has an instantaneous radius r which is less than its initial radius R. Wheel center 14 therefore lowers but it lowers further because an amount y of the workpiece is ground off. y is of course a variable which continuously increases While radius r decreases. This places the instantaneous wheel center 14 at a height h from the base line 16. Since the grinding ratio has been above defined, and also is so set forth in the parent application, as the ratio of the amount of workpiece metal removed to the amount of wheel wear, both amounts being in like volume units, such as inch 3, it may be expressed in equation form as, G=M/ W, where G is the grinding ratio, M the volume removed from the workpiece and W the wear of the wheel. Then using the dimensions designated in FIGURE 1 However, y is equal to the movement of the wheel toward the work, which is (H-h) less the reduction 1n wheel radius which is (R-r). Accordingly,

On the other hand, wheel wear W may be determined as follows:

In accordance with well known mathematical principles, the quantity within the parenthesis in Equatlon No. 3 may be expanded to its equivalent form:

Therefore, the grinding ratio M/ W may be expressed by dividing the right hand portion of Equation No. 2 by that of Equation No. 4, to give G a b (H-h) (R-r) *vrt (R -l-r) (R-r) FIGURE 2 shows equipment for determining the grinding ratio in accordance with Equation No. 5, along' with a variable speed motor means 18 which may be manually operated to regulate the speed of grinding wheel 10 as it operates on the workpiece W in accordance with the determined grinding ratio indicated, visually for example, by indicator 20. The variable quantities r and h may be continuously measured by the simultaneous operation of the two servo systems 22 and 24. Diagrammatically, wheel 10 is shown engaged with the workpiece W and these two servo systems operate during the grinding operation to effect their respective measurements. Servo 22, which constantly serves to measure the radius of wheel 10, comprises a motor M1 which drives a pinion gear 26 supported on the frame 28 on which wheel 10 is rotatably mounted as illustrated. Rotation of pinion gear 26 drives the gear rack 30 accordingly up or down. Mounted at the lower end of rack 30 is a wheel wear sensitive device 32, such as a magnetic pickup as fully described in the Coes Patents 3,062,633 and 3,064,- 396 or a capacitance pickup either of which will indicate changes in wheel radius. Of course, if a magnetic pickup is employed, wheel 10 must be made magnetically susceptible, and alternatively it must be electrically conductive to operate a capacitance type pickup.

In either case, the electrical output signal of the pickup device 32 is fed through an amplifier A1 to motor M1. As the radius of wheel 10 diminishes and gear 26 rotates, wiper 34 of potentiometer 36 is proportionately adjusted, so that the voltage between the wiper and ground thus changes in proportion to the instantaneous changes in wheel radius r.

The other servo system 24 serves to constantly measure the position of the center of wheel 10 relative to a. predetermined point of the workpiece W, such as its base; line 16, in order to provide an indication of the vary-- ing dimension h of FIGURE l. Servo system 24 includes; a motor M2 which drives a pinion gear 38 that is suitably' mounted in a fixed position as by structure 40. This gear4 cooperates with the gear rack 42 so as to move it ver-- tically relative to a position transducer or pickup 44.. Mounted on the lower end of rack 42 is a magnetic arma-y ture 46 which accordingly moves vertically within the coil 48 of the position transducer 44. Coil 48 is supported in a fixed opsition on frame 28 and consequently moves downward with the center of wheel 10. The output of coil 48 provides a signal through amplifier A2 to motor M2 which in turn adjusts the vertical position of element 48 of the position transducer via gears 38 and 42, to effect rebalance of the servo system. As such rebalance is established, the wiper 50 of potentiometer 52 is smultaneously adjusted proportionally by servo system 24, particularly by the mechanical output of motor M2 thereof,A and` accordingly. thevoltage between wiper arm 50 and ground varies inaccordance with the dimension h. l f As long as the valuesr and-rdonot'change, there is no alteration of they grinding ratio value in accordance. with Equation No. 5 for` example, and the apparatus just described will continue tooperate in its normalmanner, ile., motor 13 will'continue to rotate'wheel 10.at a given speed and neither of` the` servo` systems 22 and `24 will make any adjustments. However, as'soon as either of the parameter lr or ry changes, the grinding ratioG changes to a predetermined extent. in. accordance with `Equation No. 5,'.and'this is indicated onindicator 20.l by the computer circuitry shown vschematically. connected to the r andh potentiometer wiper arms. 34 and 5.0. The upper endsof potentiometer 36v and 52 in FIG- URE/2 are connected. to a respective sourceof voltage -l-V, which maybe of ditferent values or the same, as required, in'order that aparticular point on therespective potentiometers, such as theupper end thereof, `may respectively.V represent in4 voltage `values the initial dimensions. R and HQ. Though.lines.5,4.and 56,.which are connected respectively to the upper ends` ofA potentiometer 36 and 52, are illustrated as being xedly connected thereto, i.e. to a fixed potential point, it, should. be appreciated that these lines may` also be taps off the respective potentiometers, or otherV serially connected potentiometers (not shown), in order that the values of R and H may be changed fromL timeto time as required to Kaccommodate different size wheels and workpieces;

In accordance with I Equationy No. 5T above, the circuitryin FIGURE` 2, as in FIGURE 1l` of the said parent application `Serial, No. 253,966, includes two algebraic summers, 58 and 60, shown as respective subtractors SB for purposes of respectively taking the differences (H -h) and (R-r). Then, the diierence between those two quantities is determined by another subtractor 62 the output of which is applied to the multipiler 64. This multiplier also receives the quantity ab/ 1rt, which may be derived from one or more preset potentiometers, or other voltage sources, which provide a proper constant voltage on line 66 `to correspond scalewise to the other constant and variable voltages utilized in the computing equipment. The output of multiplier 64 is then applied to a divider 68, which receives on another input line 70 a signal corresponding to (R-l-r) (R-r), or its equivalent (R2-r2) which is derived from multiplier 72. The inputs to this multiplier are from substractor 60 and summer 74.

Divider 68 gives a continuous output signal which electrically represents the current grinding ratio. This representation is applied to a meter or the like, such as 'the grinding ratio indicator 20, whereby the grinding ratio may be continuously read by the operator of the grinding machine for example, to effect a visual comparison of `successive values of the grinding ratio. As above indicated, the grinding ratio may fall olf for certain reasons. When this is noticed on the indicator -by the operator, he merely needs to regulate the speed of wheel by controlling motor 18 in the appropriate manner to return the grinding ratio to its maximum, as by decreasing speed and consequent effect hardness of a grade of grinding Iwheel 'which has its power versus grinding ratio point normally on the reverse portion of a curve relative to other grade grinding Wheels, or by increasing the speed and consequent effective hardness of a grind-` ing Wheel Whose grade is on the forward slope of such` El CUIVC.

As a matter of example, experiments have been con ducted in accordance with this invention with Norton Company grinding wheels having .grades H through O and otherwise designated 32A461-J8VBE, the second hyphen therein being the normal place for the grade letter indication, as fully explained in the aforesaid Norton Com pany.A handbook; (The 461 itemin this specification is not described in the handbook. It describes a special purpose 4'6-lgrit abrasive used in certain Norton precision grinding wheels.) The remaining portion of these wheel markings is also fully explained therein. With No. 610 ('F.M;) steel (Rc61.0, 1:8001x 5.878" C.S.), no reversal of the performance curve for the various Igrade wheels was experienced, but it was experienced when Vega steel (Rc59.2, 1.882 x 5.923" C.S;) was yground by these wheels. Initially, the wheels were all nunon Vega steel at their recommended speed of 6000 surface feet per minute (s.f.p.m.), and the resultant aforementioned concave curve of' power versus grinding ratio was noted. Then, the two grades J 'and H, whichwere closest to the curve reversal point, were selected for operation at different speeds. The effect oflowering the speed of each of these J and K grade grinding wheels was toy increaseV the grinding ratio substantially. The maximum increase seemed to` be about three times, for example an increase in the grinding ratio from below to about 300 with relatively little change in power, for example an increase from 360 Watts of net peak power required of the inffeed driver, 'c0440 watts. The maximum performance appeared to be Iin the range of 4500-5500 s.f.|p.m. In these experiments, a Norton 6X 18 type S-3 surface grindingY machine was used with a total down feed of .020 and .040", there being 0.001 down feed per complet-e crossfeed, of the Work width, a, which crossfeed was accomplished in a series of steps at the rate of .050" per pass,V 'While the traverse rate of the wheel along the length of the work, b, was at the rate of 600 and 750l per minute respectively;

p As described and claimed by my co-company worker, Emmanuel Milias in his; application entilted, Apparatus for Increasing Grinding Ratio, filed even date herewith, it is possible to eliminate the necessity of maintaining a watch on indicator 20 to manuallly control the speed of motor 18, .by utlizing the automatic control apparatus set forth therein, and the process claims appended hereto are intended to be generic to the several varieties of alpparatus therein as well as to that disclosed herein.

From the foregoing explanation, it should be readily apparent that this invention provides the special advantage of 'substantially increasing the lgrinding ratio of a given grade grinding wheel so as to greatly improve the grinding eiciency by removing substantially more metal per volume of Iwear on the wheel. This invention therefore lls a need which cannot be accomplished through present known manufacturing techniques because thereby it is impossible to supply a grinding Wheel which has t-he required grade characteristic to maximize the grinding ratio initially let alone through the grinding operation.

It is therefore apparent that all of the objects and advantages herein mentioned, have been provided for by this invention. Yet other objects and advantages, and even modifications of this invention, will become apparent to those of ordinary skill in the art upon reading this disclosure. However, it is to be understood that the specifications of this disclosure are illustrative and not limitative, the scope of the invention being dened by the appended claims.

What is claimed is:

1. A process for improving the eiiiciency of a grinding operation by a given grade grinding wheel on a workpiece d-uring a relative rotation thereof, including the steps of: providing successive indications of the ratio of the volume of material removed from the workpiece to the volume of material worn off the grinding wheel during the grinding operation, and:

selectively changing the eiective hardness of said wheel during the grinding operation to maximize the ratio of the volume of material removed from said workpiece to the volume of material worn off said wheel during the grinding operation.

2. A process as in claim 1 wherein the effective hardness of a given grade wheel is changed yby appropriately regulating the speed of said relative rotation.

3. A process for improving the grinding operation by a given grade grinding wheel on a workpiece during relative rotation thereof including the step of:

selectively regulating a characteristic of the grinding operation according to successive indication of the grinding ratio, to maximize said ratio.

4. A process for improving the eciency of a grinding operation by a given grade grinding wheel on a workpiece during relative rotation thereof, including the step of:

selectively regulating the speed of said relative rotation, according to successive indications of the grinding ratio to maximize said ratio.

5. A process for improving the grinding operation by a given grade grinding wheel on a workpiece during relative lrotation thereof, including the steps of:

deter-mining the grinding ratio during Ithe grinding operation, and

regulating the speed of said relative rotation to increase said ratio.

6. A process as in claim wherein the step of determining the grinding ratio includes metering same and indicating successive values thereof, said speed regulating being accomplished in accordance with variations in the so indicated values.

7. A process as in claim 6 wherein the step of indicating successive grinding ratio values includes visually indicating them and the step of regulating the speed is accomplished manually.

8. A process for improving the grinding operation by a given grade grinding wheel on a workpiece during relative rotation thereof including the steps of:

determining successive grinding ratios during the said grinding operation, and

changing the speed of said relative rotation in accordance with the values of successive grinding ratios to increase the successively determined grinding ratios. 9. A process for improving the grinding operation by a given grade grinding wheel on a workpiece during relative rotation thereof, including the steps of:

determining successive grinding ratios during the said grinding operation, comparing each said ratio with the next prior one to determine which is the larger, and regulating the speed of said relative rotation to maximize successive grinding ratios by reversing the speed change direction only if the currently compared ratios show the earlier one thereof to he greater than the later one. 10. A process for improving the grinding operation by a given grade grinding wheel on a workpiece during relative rotation thereof including the steps of:

determining succesive grinding ratios during the said grinding opera-tion, and regulating the speed of said relative rotation to maximize successive grinding ratios by reversing the speed change direction only if the currently determined one of said grinding ratios is less than the next prior one thereof.

References Cited by the Examiner UNITED STATES PATENTS 1,949,975 3/1934 Reeves 51--134.5 2,168,596 8/1939 Hall 51-165 2,302,304 11/1942 Elberty 51-l34.5 2,947,121 8/1960 Coes 51-134.5

LESTER M. SWINGLE, Primary Examiner. 

1. A PROCESS FOR IMPROVING THE EFFICIENCY OF A GRINDING OPERATION BY A GIVEN GRADE GRINDING WHEEL ON A WORKPIECE DURING A RELATIVE ROTATION THEREOF, INCLUDING THE STEPS OF: PROVIDING SUCCESSIVE INDICATIONS OF THE RATIO OF THE VOLUME OF MATERIAL REMOVED FROM THE WORKPIECE TO THE VOLUME OF MATERIAL WORN OFF THE GRINDING WHEEL DURING THE GRINDING OPERATION, AND: SELECTIVELY CHANGING THE EFFECTIVE HARDNESS OF SAID WHEEL DURING THE GRINDING OPERATION TO MAXIMIZE THE RATIO OF THE VOLUME OF MATERIAL REMOVED FROM SAID WORKPIECE TO THE VOLUME OF MATERIAL WORN OFF SAID WHEEL DURING THE GRINDING OPERATION. 